Interleukin 15 (IL15 or IL15) is a vital cytokine for the activity of NK, NKT cells and CD8 T memory lymphocytes. It performs its function through a receptor consisting of 3 subunits known as α, β and γ. Subunits β and γ are common to the IL-2 receptor. The α chain of the IL15 receptor is unique to IL15 and is necessary for the cytokine's release into the extracellular medium [Duitman, E. H., et al., Mol Cell Biol, 2008. 28:4851-61] and “presents” IL15 to subunits IL15Rβ and IL15Rγ.
Due to the stimulant properties of the immune system, this interleukin has anti-tumoral properties dependent on the presence of NK cells (Suzuki, 2001, J. Leuokoc. Biol., 69:531-537) and T cells (Hazama, 1999, Br. J. Cancer., 80:1420-1426, Meazza, 2000, Int. J. Cancer, 87:574-581 and Klebanoff, 2004, Proc. Natl. Acad. Sci. USA, 2004, 101:1969-1974). IL15 is also involved in protection against viral infections and in the expansion and maintenance of a T cell-based response in immunisation and dendritic cell development.
Therefore, IL15 can be a useful therapeutic agent for treating diseases in which the immune system is involved. However, in vivo studies for the function of IL15 have been prevented partly due to the lack of availability of recombinant IL15 and to the low secretion level observed when IL15 is expressed from the native gene. Moreover, most cytokines have very low plasma half-lives given that they are produced in vivo in a local and transitory manner. Consequently, the use of IL15 in vivo requires the use of relatively high doses and frequent administration, resulting in different secondary effects which can result in cancer patients not tolerating the treatment.
With a view to overcoming these disadvantages, IL15 has been used in anti-tumoral therapy in combination with other treatments such as anti-CD40, IL-7 or IL-6 antibodies [Chou, P. C., et al., 2009, Vet Immunol Immunopathol, 130:25-34; Lin, C. Y., et al., Cancer Lett, 2008. 272(2): p. 285-95; Zhang, M., et al., Proc Natl Acad Sci USA, 2009, 106:7513-8 and Cha, E., et al., Breast Cancer Res Treat, 2009]. These combinations demonstrate a synergic effect making it possible to achieve similar effects with lower doses of IL15.
Another possibility for increasing IL 15 activity consists of co-administering it with a fusion protein that comprises the constant region of an immunoglobulin and the soluble region of the α chain of the IL 15 receptor, which produces a 50-fold increase in IL 15 activity (Rubinstein M. P. et al., 2006, Proc. Natl. Acad. Sci. USA, 103:9166-71 and Stoklasek T. A. et al., 2006, J. Immunol.; 177:6072-80).
Recently, it has been demonstrated that a polypeptide formed by amino acids 1 to 77 of the amino terminus end of the IL15 receptor a chain (the so-called “sushi domain”) is an agonist of IL15 [Mortier, E., et al., J Biol Chem, 2006. 281(3): p. 1612-9]. Thus, the administration of a fusion protein containing said domain and IL15 shows a greater antitumoral effect than that of IL15 resulting in a 65% decrease in lung metastasis of the B16F10 tumour and a reduction in the number of metastases of the HCT-116 human tumour implanted in the caecum of nude mice [Bessard, A., et al., Mol Cancer Ther, 2009. 8(9): p. 2736-45].
Another alternative to achieve improving the effect of IL15 without incurring in unwanted secondary effects consists of modifying the molecule with a view to increasing its half life. Thus, US2006257361 describes fusion proteins comprising the constant region of an immunoglobulin and IL15 presenting half lives in serum following administration higher than unmodified IL15.
Nonetheless, there is a need in the state of the art for alternative formulations of IL15 wherein the protein maintains its immune response-promoting activity but allows IL 15-related secondary effects to be reduced as much as possible.